The class of cyclic enones is well known in organic chemistry. Best known examples of cyclic-enones are quinones such as, for example, the benzoquinones, naphthoquinones, anthraquinones, phenanthraquinones, and the like. 1,4-Benzoquinone is commonly referred to as quinone. Quinones are generally brightly colored compounds and have versatile applications in chemical synthesis, biological uses, as redox materials, as well as in industry. There are several review articles on the chemistry and applications of quinones including, for example, Kirk-Othmer Encyclopedia of Chemical Technology, Third ed., Vol. 19, pages 572-605, John Wiley & Sons, New York, 1982.
The synthesis of quinones is well documented. See, for example, J. Cason, Synthesis of Benzoquinones by Oxidation, in Organic Synthesis, Vol. IV, page 305, John Wiley & Sons, New York (1948). Quinones generally are prepared by oxidizing the appropriately disubstituted aromatic hydrocarbon derivatives, the substituents being hydroxyl or amino groups in the ortho or para positions. 1,4-Benzoquinone, for example, can be made from the oxidation of hydroquinone, p-aminophenol or p-phenylenediamine, or sometimes from quinic acid. The reagents generally used for the oxidation are dichromate/sulfuric acid mixture, ferric chloride, silver (II) oxide or ceric ammonium nitrate. Such methods are generally performed in solvents which may need elaborate waste disposal procedures. Some processes may also take several hours for completion of the reaction.
Thus, some of the prior art processes utilize a catalytic agent to achieve an acceptable reaction rate while other processes proceed without catalysts. The process according to the present invention utilizes an oxidation mechanism which provides extremely high conversion, high selectivity, and fast reaction rates.
A prior art process which utilizes a catalyst in the preparation of an N-phenylquinone-imine compound is disclosed by Desmurs, et al. in U.S. Pat. No. 5,189,218. The process of Desmurs, et al., which converts a N-(4-hydroxyphenyl) aniline into N-phenylbenzoquinone-imine, utilizes a manganese, copper, cobalt, and/or nickel compound as a catalyst in an oxidation type reaction.
Other processes which convert hydroxydiphenylamines to N-phenylquinone-imines via stoichiometric oxidation using potassium or sodium dichromate catalysts are disclosed by Cottman in U.S. Pat. No. 4,968,843, U.S. Pat. No. 5,068,439, U.S. Pat. No. 5,053,540, U.S. Pat. No. 5,371,289,
EP 448,899 and EP 617,004.
Denisov, et al. (Bull. Acad. Sci. USSR Div. Chem. Sci., 37 (10), 1988) disclose preparation of N-phenylquinone-imine by reacting 4-anilino-phenol (4-hydroxydiphenylamine) with an MnO2 catalyst in a benzene solvent system.
Ram et al. (Tetrahedron, 33(8), 887-90, 1977) teach a non-catalytic autoxidation reaction process for conversion of p-hydroxydiphenylamine to N-phenyl-p-benzoquinone-imine.
The above process of Desmurs, et al., which uses a metal catalytic component, along with any other processes which utilize a metal catalyst, have several drawbacks. Not only are the metal catalysts relatively expensive, they raise important environmental concerns. For example, effluent streams and products can be contaminated by such metals. Further, recovery of the catalyst for reuse can be prohibitively expensive.
Various non-heavy metal catalysts are known in the art. For example, activated carbon catalysts, which are typically prepared by heating carbon to high temperatures (800.degree. C. to 900.degree. C.) with steam or with carbon dioxide to bring about a porous particulate structure and increased surface area, are well known oxidation catalysts. U.S. Pat. No. 4,264,776, for example, discloses and claims a process for preparing secondary amines by catalytic oxidation of tertiary amines using an activated carbon catalyst.
U.S. Pat. No. 4,158,643 teaches a method for oxidation modification of an activated carbon support in which oxygen is added to the surface of the activated carbon, and then the carbon support is impregnated with an inert hydrophobic compound. The carbon support, which may be any commercially available activated carbon for vapor phase activation use, is useful in oxidizing carbon monoxide in the presence of sulfur dioxide for an extended period of time.
U.S. Pat. No. 4,624,937 provides a method for preparing activated carbon for catalytically oxidizing tertiary amines or secondary amines in the presence of oxygen or an oxygen-containing gas to selectively produce secondary or primary amines. The method of U.S. Pat. No. 4,624,937 comprises the step of treating the carbon catalyst to remove oxides from the surface thereof.
Thus, it can be seen that processes for preparing quinoneimines from hydroxydiphenylamines are known. Additionally, the use of various carbon catalysts, including activated carbon, in chemical reactions is known. However, in the conversion of hydroxydiphenylamine to an N-phenyl-benzoquinoneimine, the use of a modified activated carbon compound as an oxidation catalyst has not heretofore been suggested.